1. Field of the Invention
The invention relates to a wavelength-converting casting composition based on a transparent epoxy casting resin which is mixed with a luminous substance, for an electroluminescent component having a body that emits ultraviolet, blue or green light.
2. Description of the Related Art
A component of that type has become known, for instance, from German published, non-prosecuted patent application DE 38 04 293. The reference describes an arrangement with an electroluminescent diode or laser diode, in which the emissions spectrum emitted by the diode is shifted toward longer wavelengths, by means of a plastic element mixed with a fluorescing, light-converting, organic colorant. The light emitted by the arrangement as a result has a different color from what the light emitting diode emitted. Depending on the type of colorant added to the plastic, it is possible to produce LED arrays that light up in different colors with one and the same type of light-emitting diode (LED).
In many potential applications for LEDs, such as in display elements in motor vehicle dashboards, illumination in aircraft and automobiles, and in LED displays capable of showing full color, there is an increasing demand for LED arrays with which mixed color light and in particular white light can be generated.
However, the prior art casting compositions of the type referred to at the outset with organic luminous substances exhibit a shift in the color location, that is, the color of the light emitted by the electroluminescent component, under temperature and temperature/humidity stresses. Japanese patent disclosure JP-07 176 794-A describes a white-light-emitting planar light source, in which two diodes that emit blue light are disposed on one face end of a transparent plate and emit light into the transparent plate. The transparent plate is coated on one of the two opposed main sides with a fluorescing substance that emits light when it is excited with the blue light of the diodes. The light emitted by the fluorescing substance has a different wavelength from the blue light emitted by the diodes. In this known component, it is especially difficult to apply the fluorescing substance in such a way that the light source emits homogeneous white light. Moreover, replicability and mass production presents major problems, because even slight fluctuations in the layer thickness of the fluorescing layer, for instance from irregularities of the surface of the transparent plate, cause a change in the white of the light emitted.